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# Category Archives: Problems

## A numerical from Projectile motion, friction and more

**Hale asked:**

One side of the roof of a building slopes up at 33.5°. A roofer kicks a round, flat rock that has been thrown onto the roof by a neighborhood child. The rock slides straight up the incline with an initial speed of 15.0 m/s. The coefficient of kinetic friction between the rock and the roof is 0.430. The rock slides 10.0 m up the roof to its peak. It crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof, with negligible air resistance. Determine the maximum height the rock reaches above the point where it was kicked.

**(The question is left for visitors to answer.)**

## A question from kinematics – motion in one dimension

Natasha Sehgal Asked:

“A stone is thrown in a vertically upward direction with a velocity of 5m/s. If the acceleration of the stone during its motion is 10m/s^2 in the downward direction , what will be the height attained by the stone and how much time will it take to reach there?”

Answer:

Take,

u=5m/s

a= -10 m/s^{2}

v=0 at the topmost position

S= H_{max} = ?

The eqn of motion to use

v^{2} – u^{2} = 2aS

Which gives H = 1.25 m

From the eqn

v=u + at

t= 0.5 s